.TH RUBY 1 "Ruby Programmers Reference Guide" "November 7, 2012" "UNIX"
.SH NAME
\fBruby\fP
\- Interpreted object-oriented scripting language
.SH SYNOPSIS
.br
\fBruby\fP
[\fB\--copyright\fP]
[\fB\--version\fP]
[\fB\-SUacdlnpswvy\fP]
[\fB\-0\fP[\fIoctal\fP]]
[\fB\-C\fP \fIdirectory\fP]
[\fB\-E\fP \fIexternal\fP[]]:\fIinternal\fP
[\fB\-F\fP \fIpattern\fP]
[\fB\-I\fP \fIdirectory\fP]
[\fB\-K\fP \fIc\fP]
[\fB\-T\fP[\fIlevel\fP]]
[\fB\-W\fP[\fIlevel\fP]]
[\fB\-e\fP \fIcommand\fP]
[\fB\-i\fP[\fIextension\fP]]
[\fB\-r\fP \fIlibrary\fP]
[\fB\-x\fP[\fIdirectory\fP]]
[-Bro \fBenable\fP|\fBdisable\fP Brc-\fIFEATURE\fP]
[\fB\--dump\fP=\fItarget\fP]
[\fB\--verbose\fP]
[\fB\--\fP]
[\fIprogram_file\fP]
[\fIargument\fP ...]
.SH DESCRIPTION
Ruby is an interpreted scripting language for quick and easy
object-oriented programming.  It has many features to process text
files and to do system management tasks (like in Perl).  It is simple,
straight-forward, and extensible.

If you want a language for easy object-oriented programming, or you
don't like the Perl ugliness, or you do like the concept of LISP, but
don't like too many parentheses, Ruby might be your language of
choice.
.SH FEATURES
Ruby's features are as follows:
.TP
.B "Interpretive"
Ruby is an interpreted language, so you don't have to recompile
programs written in Ruby to execute them.

.TP
.B "Variables have no type (dynamic typing)"
Variables in Ruby can contain data of any type.  You don't have to
worry about variable typing.  Consequently, it has a weaker compile
time check.

.TP
.B "No declaration needed"
You can use variables in your Ruby programs without any declarations.
Variable names denote their scope - global, class, instance, or local.

.TP
.B "Simple syntax"
Ruby has a simple syntax influenced slightly from Eiffel.

.TP
.B "No user-level memory management"
Ruby has automatic memory management.  Objects no longer referenced
from anywhere are automatically collected by the garbage collector
built into the interpreter.

.TP
.B "Everything is an object"
Ruby is a purely object-oriented language, and was so since its
creation.  Even such basic data as integers are seen as objects.

.TP
.B "Class, inheritance, and methods"
Being an object-oriented language, Ruby naturally has basic
features like classes, inheritance, and methods.

.TP
.B "Singleton methods"
Ruby has the ability to define methods for certain objects.  For
example, you can define a press-button action for certain widget by
defining a singleton method for the button.  Or, you can make up your
own prototype based object system using singleton methods, if you want
to.

.TP
.B "Mix-in by modules"
Ruby intentionally does not have the multiple inheritance as it is a
source of confusion.  Instead, Ruby has the ability to share
implementations across the inheritance tree.  This is often called a
`Mix-in'.

.TP
.B "Iterators"
Ruby has iterators for loop abstraction.

.TP
.B "Closures"
In Ruby, you can objectify the procedure.

.TP
.B "Text processing and regular expressions"
Ruby has a bunch of text processing features like in Perl.

.TP
.B "M17N, character set independent"
Ruby supports multilingualized programming. Easy to process texts
written in many different natural languages and encoded in many
different character encodings, without dependence on Unicode.

.TP
.B "Bignums"
With built-in bignums, you can for example calculate factorial(400).

.TP
.B "Reflection and domain specific languages"
Class is also an instance of the Class class. Definition of classes and methods
is an expression just as 1+1 is. So your programs can even write and modify programs.
Thus you can write your application in your own programming language on top of Ruby.

.TP
.B "Exception handling"
As in Java(tm).

.TP
.B "Direct access to the OS"
Ruby can use most
UNIX
system calls, often used in system programming.

.TP
.B "Dynamic loading"
On most
UNIX
systems, you can load object files into the Ruby interpreter
on-the-fly.
.TP
.B "Rich libraries"
Libraries called "builtin libraries" and "standard libraries" are bundled with Ruby.
And you can obtain more libraries via the package management system called `RubyGems'.

Moreover there are thousands of Ruby projects on GitHub
<\fIhttps://github.com/languages/Ruby\fP.>

.SH OPTIONS
Ruby interpreter accepts following command-line options (switches).
They are quite similar to those of
\fBperl\fP(1).

.TP
\fB\--copyright\fP
Prints the copyright notice.

.TP
\fB\--version\fP
Prints the version of Ruby interpreter.

.TP
\fB\-0\fP[\fIoctal\fP]
(The digit
``zero''.)
Specifies the input record separator
("$/")
as an octal number. If no digit is given, the null character is taken
as the separator.  Other switches may follow the digits.
\fB\-00\fP
turns Ruby into paragraph mode.
\fB\-0777\fP
makes Ruby read whole file at once as a single string since there is
no legal character with that value.

.TP
\fB\-C\fP \fIdirectory\fP
.TP
\fB\-X\fP \fIdirectory\fP
Causes Ruby to switch to the directory.

.TP
\fB\-E\fP \fIexternal\fP[]:\fIinternal\fP
.TP
\fB\--encoding\fP \fIexternal\fP[]:\fIinternal\fP
Specifies the default value(s) for external encodings and internal encoding. Values should be separated with colon (:).

You can omit the one for internal encodings, then the value
("Encoding.default_internal") will be nil.

.TP
\fB\--external-encoding\fP=\fIencoding\fP
.TP
\fB\--internal-encoding\fP=\fIencoding\fP
Specify the default external or internal character encoding

.TP
\fB\-F\fP \fIpattern\fP
Specifies input field separator
("$;").

.TP
\fB\-I\fP \fIdirectory\fP
Used to tell Ruby where to load the library scripts.  Directory path
will be added to the load-path variable
("$:").

.TP
\fB\-K\fP \fIkcode\fP
Specifies KANJI (Japanese) encoding. The default value for script encodings
("__ENCODING__") and external encodings ("Encoding.default_external") will be the specified one.
\fIkcode\fP
can be one of
.TP
.B e
EUC-JP

.TP
.B s
Windows-31J (CP932)

.TP
.B u
UTF-8

.TP
.B n
ASCII-8BIT (BINARY)

.TP
\fB\-S\fP
Makes Ruby use the
.IR PATH
environment variable to search for script, unless its name begins
with a slash.  This is used to emulate
#!
on machines that don't support it, in the following manner:

#! /usr/local/bin/ruby
.br
# This line makes the next one a comment in Ruby \e
.br
  exec /usr/local/bin/ruby -S $0 $*
.br

.TP
\fB\-T\fP[\fIlevel=1\fP]
Turns on taint checks at the specified level (default 1).

.TP
\fB\-U\fP
Sets the default value for internal encodings
("Encoding.default_internal") to UTF-8.

.TP
\fB\-W\fP[\fIlevel=2\fP]
Turns on verbose mode at the specified level without printing the version
message at the beginning. The level can be;
.TP
.B 0
Verbose mode is "silence". It sets the
"$VERBOSE"
to nil.

.TP
.B 1
Verbose mode is "medium". It sets the
"$VERBOSE"
to false.

.TP
.B 2 (default)
Verbose mode is "verbose". It sets the
"$VERBOSE"
to true.
\fB\-W\fP
2 is same as
\fB\-w\fP

.TP
\fB\-a\fP
Turns on auto-split mode when used with
\fB\-n\fP
or
\fB\-p\fP.
In auto-split mode, Ruby executes
.nf
\&  $F = $_.split
.fi
at beginning of each loop.

.TP
\fB\-c\fP
Causes Ruby to check the syntax of the script and exit without
executing. If there are no syntax errors, Ruby will print
``Syntax OK''
to the standard output.

.TP
\fB\-d\fP
.TP
\fB\--debug\fP
Turns on debug mode.
"$DEBUG"
will be set to true.

.TP
\fB\-e\fP \fIcommand\fP
Specifies script from command-line while telling Ruby not to search
the rest of the arguments for a script file name.

.TP
\fB\-h\fP
.TP
\fB\--help\fP
Prints a summary of the options.

.TP
\fB\-i\fP \fIextension\fP
Specifies in-place-edit mode.  The extension, if specified, is added
to old file name to make a backup copy.  For example:

% echo matz > /tmp/junk
.br
% cat /tmp/junk
.br
matz
.br
% ruby -p -i.bak -e '$_.upcase!' /tmp/junk
.br
% cat /tmp/junk
.br
MATZ
.br
% cat /tmp/junk.bak
.br
matz
.br

.TP
\fB\-l\fP
(The lowercase letter
``ell''.)
Enables automatic line-ending processing, which means to firstly set
"$\e"
to the value of
"$/",
and secondly chops every line read using
chop!.

.TP
\fB\-n\fP
Causes Ruby to assume the following loop around your script, which
makes it iterate over file name arguments somewhat like
\fBsed\fP
\fB\-n\fP
or
\fBawk\fP.

while gets
.br
  ...
.br
end
.br

.TP
\fB\-p\fP
Acts mostly same as -n switch, but print the value of variable
"$_"
at the each end of the loop.  For example:

% echo matz | ruby -p -e '$_.tr! "a-z", "A-Z"'
.br
MATZ
.br

.TP
\fB\-r\fP \fIlibrary\fP
Causes Ruby to load the library using require.  It is useful when using
\fB\-n\fP
or
\fB\-p\fP.

.TP
\fB\-s\fP
Enables some switch parsing for switches after script name but before
any file name arguments (or before a
\fB\--\fP).
Any switches found there are removed from
ARGV
and set the corresponding variable in the script.  For example:

#! /usr/local/bin/ruby -s
.br
# prints "true" if invoked with `-xyz' switch.
.br
print "true\en" if $xyz
.br

On some systems
"$0"
does not always contain the full pathname, so you need the
\fB\-S\fP
switch to tell Ruby to search for the script if necessary (to handle embedded
spaces and such).  A better construct than
"$*"
would be
${1+"$@"},
but it does not work if the script is being interpreted by
\fBcsh\fP(1).

.TP
\fB\-v\fP
Enables verbose mode.  Ruby will print its version at the beginning
and set the variable
"$VERBOSE"
to true.  Some methods print extra messages if this variable is true.
If this switch is given, and no other switches are present, Ruby quits
after printing its version.

.TP
\fB\-w\fP
Enables verbose mode without printing version message at the
beginning.  It sets the
"$VERBOSE"
variable to true.

.TP
\fB\-x\fP[\fIdirectory\fP]
Tells Ruby that the script is embedded in a message.  Leading garbage
will be discarded until the first line that starts with
``#!''
and contains the string,
``ruby''.
Any meaningful switches on that line will be applied.  The end of the script
must be specified with either
EOF,
"^D" ("control-D"),
"^Z" ("control-Z"),
or the reserved word
__END__.
If the directory name is specified, Ruby will switch to that directory
before executing script.

.TP
\fB\-y\fP
.TP
\fB\--yydebug\fP
DO NOT USE.

Turns on compiler debug mode.  Ruby will print a bunch of internal
state messages during compilation.  Only specify this switch you are going to
debug the Ruby interpreter.

.TP
\fB\--disable-\fP\fIFEATURE\fP
.TP
\fB\--enable-\fP\fIFEATURE\fP
Disables (or enables) the specified
\fIFEATURE\fP
\&.
.TP
\fB\--disable-gems\fP
.TP
\fB\--enable-gems\fP
Disables (or enables) RubyGems libraries.  By default, Ruby will load the latest
version of each installed gem. The
Gem
constant is true if RubyGems is enabled, false if otherwise.

.TP
\fB\--disable-rubyopt\fP
.TP
\fB\--enable-rubyopt\fP
Ignores (or considers) the
.IR RUBYOPT
environment variable. By default, Ruby considers the variable.

.TP
\fB\--disable-all\fP
.TP
\fB\--enable-all\fP
Disables (or enables) all features.


.TP
\fB\--dump\fP=\fItarget\fP
DO NOT USE.

Prints the specified target.
\fItarget\fP
can be one of;
.TP
.B insns
disassembled instructions


Only specify this switch if you are going to debug the Ruby interpreter.

.TP
\fB\--verbose\fP
Enables verbose mode without printing version message at the
beginning.  It sets the
"$VERBOSE"
variable to true.
If this switch is given, and no other switches are present, Ruby quits
after printing its version.

.SH ENVIRONMENT
.TP
.B RUBYLIB
A colon-separated list of directories that are added to Ruby's
library load path
("$:"). Directories from this environment variable are searched
before the standard load path is searched.

e.g.:
.nf
\&  RUBYLIB="$HOME/lib/ruby:$HOME/lib/rubyext"
.fi

.TP
.B RUBYOPT
Additional Ruby options.

e.g.
.nf
\&  RUBYOPT="-w -Ke"
.fi

Note that RUBYOPT can contain only
\fB\-d\fP,\fB\-E\fP,\fB\-I\fP,\fB\-K\fP,\fB\-r\fP,\fB\-T\fP,\fB\-U\fP,\fB\-v\fP,\fB\-w\fP,\fB\-W,\fP \fB\--debug\fP,
\fB\--disable-\fP\fIFEATURE\fP
and
\fB\--enable-\fP\fIFEATURE\fP.

.TP
.B RUBYPATH
A colon-separated list of directories that Ruby searches for
Ruby programs when the
\fB\-S\fP
flag is specified.  This variable precedes the
.IR PATH
environment variable.

.TP
.B RUBYSHELL
The path to the system shell command.  This environment variable is
enabled for only mswin32, mingw32, and OS/2 platforms.  If this
variable is not defined, Ruby refers to
.IR COMSPEC.

.TP
.B PATH
Ruby refers to the
.IR PATH
environment variable on calling Kernel#system.

And Ruby depends on some RubyGems related environment variables unless RubyGems is disabled.
See the help of
\fBgem\fP(1)
as below.

% gem help
.br

.SH GC ENVIRONMENT
The Ruby garbage collector (GC) tracks objects in fixed-sized slots,
but each object may have auxillary memory allocations handled by the
malloc family of C standard library calls (
\fBmalloc\fP(3),
\fBcalloc\fP(3),
and
\fBrealloc\fP(3))
In this documentatation, the "heap" refers to the Ruby object heap
of fixed-sized slots, while "malloc" refers to auxillary
allocations commonly referred to as the "process heap".
Thus there are at least two possible ways to trigger GC:
.TP
.B 1
Reaching the object limit.
.TP
.B 2
Reaching the malloc limit.

In Ruby 2.1, the generational GC was introduced and the limits are divided
into young and old generations, providing two additional ways to trigger
a GC:
.TP
.B 3
Reaching the old object limit.
.TP
.B 4
Reaching the old malloc limit.

There are currently 4 possible areas where the GC may be tuned by
the the following 11 environment variables:
.TP
.B RUBY_GC_HEAP_INIT_SLOTS
Initial allocation slots.  Introduced in Ruby 2.1, default: 10000.

.TP
.B RUBY_GC_HEAP_FREE_SLOTS
Prepare at least this amount of slots after GC.
Allocate this number slots if there are not enough slots.
Introduced in Ruby 2.1, default: 4096

.TP
.B RUBY_GC_HEAP_GROWTH_FACTOR
Increase allocation rate of heap slots by this factor.
Introduced in Ruby 2.1, default: 1.8, minimum: 1.0 (no growth)

.TP
.B RUBY_GC_HEAP_GROWTH_MAX_SLOTS
Allocation rate is limited to this number of slots,
preventing excessive allocation due to RUBY_GC_HEAP_GROWTH_FACTOR.
Introduced in Ruby 2.1, default: 0 (no limit)

.TP
.B RUBY_GC_HEAP_OLDOBJECT_LIMIT_FACTOR
Perform a full GC when the number of old objects is more than R * N,
where R is this factor and N is the number of old objects after the
last full GC.
Introduced in Ruby 2.1.1, default: 2.0

.TP
.B RUBY_GC_MALLOC_LIMIT
The initial limit of young generation allocation from the malloc-family.
GC will start when this limit is reached.
Default: 16MB

.TP
.B RUBY_GC_MALLOC_LIMIT_MAX
The maximum limit of young generation allocation from malloc before GC starts.
Prevents excessive malloc growth due to RUBY_GC_MALLOC_LIMIT_GROWTH_FACTOR.
Introduced in Ruby 2.1, default: 32MB.

.TP
.B RUBY_GC_MALLOC_LIMIT_GROWTH_FACTOR
Increases the limit of young generation malloc calls, reducing
GC frequency but increasing malloc growth until RUBY_GC_MALLOC_LIMIT_MAX
is reached.
Introduced in Ruby 2.1, default: 1.4, minimum: 1.0 (no growth)

.TP
.B RUBY_GC_OLDMALLOC_LIMIT
The initial limit of old generation allocation from malloc,
a full GC will start when this limit is reached.
Introduced in Ruby 2.1, default: 16MB

.TP
.B RUBY_GC_OLDMALLOC_LIMIT_MAX
The maximum limit of old generation allocation from malloc before a
full GC starts.
Prevents excessive malloc growth due to RUBY_GC_OLDMALLOC_LIMIT_GROWTH_FACTOR.
Introduced in Ruby 2.1, default: 128MB

.TP
.B RUBY_GC_OLDMALLOC_LIMIT_GROWTH_FACTOR
Increases the limit of old generation malloc allocation, reducing full
GC frequency but increasing malloc growth until RUBY_GC_OLDMALLOC_LIMIT_MAX
is reached.
Introduced in Ruby 2.1, default: 1.2, minimum: 1.0 (no growth)

.SH STACK SIZE ENVIRONMENT
Stack size environment variables are implementation-dependent and
subject to change with different versions of Ruby.  The VM stack is used
for pure-Ruby code and managed by the virtual machine.  Machine stack is
used by the operating system and its usage is dependent on C extensions
as well as C compiler options.  Using lower values for these may allow
applications to keep more Fibers or Threads running; but increases the
chance of SystemStackError exceptions and segmentation faults (SIGSEGV).
These environment variables are available since Ruby 2.0.0.
All values are specified in bytes.

.TP
.B RUBY_THREAD_VM_STACK_SIZE
VM stack size used at thread creation.
default: 131072 (32-bit CPU) or 262144 (64-bit)

.TP
.B RUBY_THREAD_MACHINE_STACK_SIZE
Machine stack size used at thread creation.
default: 524288 or 1048575

.TP
.B RUBY_FIBER_VM_STACK_SIZE
VM stack size used at fiber creation.
default: 65536 or 131072

.TP
.B RUBY_FIBER_MACHINE_STACK_SIZE
Machine stack size used at fiber creation.
default: 262144 or 524288

.SH SEE ALSO
.TP
https://www.ruby-lang.org/
The official web site.
.TP
https://www.ruby-toolbox.com/
Comprehensive catalog of Ruby libraries.

.SH REPORTING BUGS
Security vulnerabilities should be reported via an email to
<security@ruby-lang.org>
Reported problems will be published after they've been fixed.

And you can report other bugs and feature requests via the
Ruby Issue Tracking System (https://bugs.ruby-lang.org/).
Do not report security vulnerabilities
via the system because it publishes the vulnerabilities immediately.
.SH AUTHORS
Ruby is designed and implemented by
Yukihiro Matsumoto <matz@netlab.jp>.

See
<\fIhttps://bugs.ruby-lang.org/projects/ruby/wiki/Contributors\fP>
for contributors to Ruby.
